rmm's are very good with a wide selection, his later (higher number) speed trees are excellent. However, his trees are not seasonal so, if that is important to you, you may decide to only use his evergreens.
roystrainz' payware are very good also and are seasonal. Again, his later trees sets are better than his earlier offerings.
mcguirel's freeware is also very good although not seasonal for the most part. Her payware is excellent if you were fortunately enough to acquire it. She spent a great deal of effort minimizing the billboard pop for the distant LOD transition as well as lowering triangle count.
profig's have a remarkably low triangle count but are not seasonal
Auran and gawpo50's are lovely at near distance and are seasonal, however they both have an unfortunate pop at the billboard transition and don't look all that good at that distance and beyond.
jankvis' payware/freeware trees are uneven, some are amazing, some are just weird. They have a rather high triangle count for the most part but are seasonal and have an excellent billboard transition.
olegkhim's are nice but non-seasonal, very good billboard transition.
I have some 1900 speedtree assets installed (many faulty) and it is fun finding exactly the right mix for a given route. You can spend some time looking at these in Preview Asset and get some idea of how good the LOD transitions are, how many triangles they have, and how good the seasonal aspects are.
It is my understanding that there is a wind setting somewhere in trainz but I have not looked into it.